/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 张宇田
 * Date: 2025-06-08
 * Time: 22:05
 */
import java.util.*;

public class TravelBudget {
    //油站
    static class Station implements Comparable<Station> {
        //距离出发点的距离 油价
        double dist, price;
        Station(double dist, double price) {
            this.dist = dist;
            this.price = price;
        }

        public int compareTo(Station o) {
            return Double.compare(this.dist, o.dist);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        double C = sc.nextDouble();     // 油箱容量
        double D = sc.nextDouble();     // 总距离
        double d = sc.nextDouble();     // 每升能跑的距离
        double P = sc.nextDouble();     // 起点油价
        int N = sc.nextInt();           // 油站数量

        List<Station> list = new ArrayList<>();
        list.add(new Station(0, P));    // 起点加进去
        //把起点当做一个油站 初始位置为0

        //把所有油站都存到链表里面
        for (int i = 0; i < N; i++) {
            double p = sc.nextDouble();
            double dis = sc.nextDouble();
            list.add(new Station(dis, p));

        }

        list.add(new Station(D, 0));    // 终点作为一个油站

        Collections.sort(list);

        //如果第一个油站距离不为0 说明没有加油的地方
        if (list.get(0).dist != 0) {
            System.out.println("No Solution");
            return;
        }


        double sum = 0;        // 总花费
        double tank = 0;       // 当前油量
        int now = 0;           //当前所在油站下标
        int end = list.size() - 1;
        double maxDis = C * d; // 一箱油能跑的最远距离
        //没有找到终点站就继续往下走
        while (now < end) {
            //下一站，没找到就记录为-1
            int next = -1;
            //最便宜的站
            double minP = Double.MAX_VALUE;

            // 寻找下一个站
            for (int i = now + 1; i < list.size() &&
                    list.get(i).dist - list.get(now).dist <= maxDis; i++) {
                //下一个油站离出发点的距离 - 当前油站离出发点的距离 小于等于 能跑的最大距离 就可以继续循环
                if (list.get(i).price < minP) {
                    minP = list.get(i).price;
                    next = i;
                    if (minP < list.get(now).price)
                        break; // 找到更便宜的，就赶紧去 ， 后面的没准更贵
                }
            }

            if (next == -1) {
                System.out.printf("No Solution");
                return;
            }
            //距离/每升油能跑多远 = 所需多少油
            double need = (list.get(next).dist - list.get(now).dist) / d;
            //如果下一站的油比这一站便宜， 就不加油了
            if (minP < list.get(now).price) {
                //邮箱的油不够
                if (tank < need) {
                    sum += (need - tank) * list.get(now).price;
                    tank = 0;
                } else {
                    tank -= need;
                }
            } else {
                //更贵就加满
                sum += (C - tank) * list.get(now).price;
                tank = Math.max(0, C - need);

            }

            now = next;
        }

        System.out.printf("%.2f", sum);
    }
}
